Extraction of oil from oil shales and like oil bearing material



Nov. 3, 1959 G. R. COULSON 2,911,349 EXTRACTION OF OIL. FROM OIL SHALES AND LIKE OIL BEARING MATERIAL Filed May 16, 1957 pyRoa/rz/Mm/aw .SHALE CRUSH/N6 & PRE'HEAT/NG SUPER-HEATED STEAM PRESSURE DISINTEGRA r/0N COOLER o/s msma AGENT D/L uszvr WATER CENTR/F'UGAL SEPARATION MINERAL souos 4 WAFER aromas INVENTOR Gordon A! Couison ma mwgfim ATTORNEY$ 2,911,349 Patented Nov. 3, 1959 EXTRACTION OF OIL FROM OIL SHALES AND LIKE OIL BEARING MATERIAL Gordon R. Coulson, Calgary, Alberta, Canada, assignor to Can-Amera Oil Sanas Development Ltd., Calgary, Alberta, Canada Application May 16, 1957, Serial No. 659,471

Claims. (Cl. 208-41) This invention relates to a process for separating oil from oil shales. More particularly it relates to a process for separating liquid, semi-liquid or solid bituminous materials from oil shales. The type of shales contemplated for treatment herein are the so-called asphaltic pyrobitumens or pyrobituminous shales wherein the organic constituents are characterized in their natural state by relatively low solubility in hydrocarbon solvents and from which the oil values are customarily recoverable by retorting methods involving destructive distillation to produce tars, lower boiling liquid hydrocarbons and gases.

The present invention distinguishes from my copending application Serial No. 625.251, filed November 30, 1956, now US. Patent No. 2,825677, in the character of the raw materials undergoing treatment, and particularly in the initial processing steps. My copending application discloses and claims a method for treating the so-called tar sands, shales and other relatively porous and/or loosely consolidated minerals, in which the oil or tar not only surrounds the oil particles but tends to fill the interstices. The oils recoverable from such materials are highly viscous liquids or semi-liquids closely resembling crude petroleum.

The raw materials to be treated by the present invention are sometimes referred to as oil forming shales wherein the pyrobitumens are associated with earthy matter. The shale is a compact solid capable of being disintegrated into very fine particles. These shales occur in many places in the world including Scotland, England, New Zealand, New Brunswick, Nova Scotia, certain parts of the Eastern United States, and in Utah, Colorado, Wyoming and elsewhere. Heretofore the oils have generally been recovered therefrom by one form or am other of destructive distillation. While in Europe some of the deposits have been worked and the oil recovered on a commercial scale by this method, recovery of shale oil in North America is still in a development stage. While numerous modifications of the destructive distillation process have been devised, the processes in general comprise breaking the relatively soft shale into lumps and introducing them into the top of a vertical retort. Steam and air is introduced at the bottom of the bed so that combustion of some of the organic matter occurs. The temperatures at the bottom of the retorts may be of the order of 1400-1500 F., under which conditions part of the steam reacts with coke remaining on the spent shale particles. The hot gases rising through the bed of shale raises the temperature to the order of 9001000 P. which causes destructive distillation. The gas and normally liquid distillation products including a certain amount of naphtha and shale tar, are recovered. Coke like material remaining on the shale serves as a source of fuel for the operation.

The socalled shale oils at ordinary temperatures may be solid or semi-solid, often having a ring and ball fusing point of about 75-115 F. Although the organic material as it occurs in the original shale is comparatively insoluble in most solvents, the oil recovered from the retorting process is soluble in gasoline and other hydrocarbon solvents. It has been proposed to subject shale to the action of liquid water at temperatures above 500 F. and pressures adequate to maintain the water in liquid phase. This is said to disintegrate the shale into a clay like mass from which the oil is separated by gravity or by solvent extraction.

It has also been proposed to digest the shale at high temperatures with previously recovered shale oil, the spent shale being washed with solvent to complete the recovery.

Neither of these processes appear to have attained any degree of recognition, and the present day development continues along the line of destructive distillation.

Since the shales contain considerable amounts of nitrogen compounds, ammonia is produced during the retorting and is recovered in substantial amounts usually as ammonium sulfate by scrubbing the off gases with dilute sulfuric acid. The oils contain sulfur generally in amounts of 1.52.5% or more, and from about 1 to about 5% oxygen. Thus the oils are somewhat different from the usual crude petroleum oils or the oils recovered from the so-called tar sands. However once they are recovered they can be converted by suitable cracking and refining methods into motor fuel and other products to which ordinary petroleum is converted.

The attached figure diagrammatically represents one embodiment of the invention. This will be evident from the figure itself and from the following description so that a separate description of the figure is not required.

According to a broad embodiment my invention comprises heating and crushing the shale to a size convenient for handling, heating the particles by contact with superheated steam at a temperature of about 570-1200 F. and usually from about 650 to about 800 F., and at a superatmospheric pressure below the critical pressure of water. Thus, at 705 F. a pressure below 3206 p.s.i.g. would be employed. The superheated steam causes the particles to disintegrate into relatively fine, dry powder. While disintegration will occur at pressures as low as about p.s.i.g. it is much more rapid at higher pressures. Each of the particles is covered by a thin layer of oil. The oil does not separate during this treatment but is found to be in a soluble form. The oilbea.ring powder is general cooled to a temperature below the boiling point of water (212 F.), and a dispersing agent such as sodium silicate and/ or a wetting agent or surface active material such as the alkyl benzene sulfonates, alkali metal salts of sulfated or sulfonated long chain fatty alcohols, long chain fatty acid amide esters such as the polyoxyalkylene amides of C -C fatty acids, and many others, may be used.

If the shale oil is not liquid (shale oils are frequently somewhat waxy) or is too viscous at the subsequent processing temperature, or if the specific gravity is greater than 0.95, a suitable diluent or solvent for the oil is added to reduce its specific gravity to a point below about 0.95 when measured at a temperature of 77 F. and to render the finally recovered oil fluid.

Sutficient liquid water or a solution of a neutral salt in water is added to fill the interstices between the solid particles, plus enough water to form a barrier between the solids and the oil which is subsequently separated. The mixture is a fluid slurry, and is then subjected to centrifugal force, usually at ambient temperature, but in any event below 210 F. and above the freezing point of the aqueous phase, to separate the finely divided particles of solids saturated with water and substantially oil-free, as a bottom layer. The diluted oil, substantially solids-free, forms an upper layer which is maintained out of contact with the layer of solid material by an inter vening barrier of water which is usually at least one inch thick. This prevents the oil and solids from again coming into contact. The oil layer is recovered from the centrifuge substantially free of water and solids. It can be transported as a liquid through pipe lines, or by truck or tank, and can be processed into gas, gasoline, and coke, according to conventional methods with or without removal of the solvent.

I have found that upon treatment, frequently with agitation, of the oil shale which may be crushed to convenient size, for example, one inch in diameter and smaller, with superheated steam at the elevated temperatures and pressures, the shale disintegrates into very fine particles resembling talcum powder. In many instances the individual particles are silica. Because of the fineness of the individual particles the oil is adsorbed as a thin film, possibly only a few molecules in thickness. In this re spect it diflFers markedly from the tar sands referred to in my copending application.

The method of heating which is preferred consists of heating the oil shale at a temperature above about 570 F. and preferably in the neighborhood of "IOU-800 F. with superheated steam. The operating conditions of time and temperature are chosen so that no substantial cracking or breakdown to gas and coke occurs. The steam may serve to heat up the oil shale to the proper processing temperature, or the shale may be preheated in any suitable manner, as by indirect heat exchange, for example, with hot previously processed shale. The pressure employed is any pressure up to the critical pressure of the steam at the processing temperature so as to insure that it is substantially in the vapor phase when the shale reaches the opertaing temperature. The operation may be carried out in any suitable apparatus such as a rotating drum or kiln, or a vessel equipped with agitators. Another type is the so-called fluidized solids operation in which the steam agitates the particles and keeps them in a condition of suspension resembling a boiling liquid. This reduces the shale to the fine powder previously referred to.

Whether significant changes occur in the oil or not, is not known. However, the oil is converted to a soluble form and one readily susceptible to the subsequent steps of the process. The actual pressures may range preferably from about 1200 to about 3200 p.s.i.g., corresponding to the saturation temperature desired. However, lower or higher pressures may be used providing the steam remains as such and is not liquefied to any substantial extent. The time required for the disintegration is usually short so that little or no thermal cracking of the oil occurs. At pressures approaching 3000 p.s.i.g. or higher the disintegration is very rapid, requiring only a few seconds. At l50500 p.s.i.g., the disintegration requires a longer time, say from 0.5-5 minutes. The temperature employed and the composition of the oil shale may be factors aflecting the time required.

The powder is immediately withdrawn from the system and cooled by, for example, heat exchange with fresh feed, or by other suitable means, such as quenching with water or other suitable quenching agent, preferably to about 60l50 F. The hot disintegrated shale should be cooled as rapidly as possible to a temperature below that at which substantial cracking occurs in order to eflect the maximum recovery of oil therefrom. A dispersing and/ or wetting agent is added as previously mentioned. Since the final separation of the oil is usually by means of centrifuge and in the presence of liquid water, the temperature should be below that at which water boils and may be anywhere above its freezing point. Suitable temperatures of about 70" F. to about 100 F. are used, there being no point to further cooling, and moreover, the viscosity of the oil increases at lower temperatures which may make the separation more difiicult. There should not be substantial amounts of free oxygen in contact with 4 l the shale until it has reached a temperature below about 350-400 F.

Since the oil usually has a relatively high specific gravity, is viscous, and in many instances is solid or semisolid, possibly due to the presence of waxy parafiins, a diluent is usually added. These may comprise relatively low boiling hydrocarbons or fractions of hydrocarbon dis tillates. While relatively low boiling, normally liquid hydrocarbons such as benzene, xylene, toluene, gasoline, eithercracked or straight run, petroleum naphtha, coal tar naphtha, and the like may be employed, it is preferred to use solvents having initial boiling points of about 350400 F. and end boiling points below about 750 F. Suitable solvents or diluents boil at about 400- 600 F., in the kerosene or light gas oil range. This minimizes loss of solvent due to evaporation. A highly suitable diluent is one of the preferred boiling range which is obtained by cracking or coking of the recovered oil. Waxy fractions of the product, which are solid or semisolid at the centrifuging temperature should not be used. When the lower boiling diluents are used, a vapor proof system should be employed to avoid loss by evaporation. With higher boiling diluents such as those referred to this is a less serious problem. Oils of an aromatic or olefinic character are particularly most eflicacious since certain of the constituents are more soluble in these than in predominantly paraflinic distillates. Light recycle oils from catalytic and thermal cracking and catalytic reforming are high in aromatic hydrocarbon content and consequently are especially suitable diluents. These usually boil in the heavy naphtha or light gas oil range, say 300 F.700 F. and preferably about 350 F. to 600 F.

Moreover, it is sometimes of advantage to recycle a portion of the recovered oil mixed with the diluent since in some instances this appears to increase the ultimate recovery of oil from the shale. This also reduces the proportion of diluent used. The diluents boil below the recovered oil and may be separated by distillation and reused if desired, or may be left in the oil. The amount of diluent must be suflicient to reduce the specific gravity of the separated oil to a point within the range of about 0.75 to about 0.95. Some of the oils recovered from the shale have sufiiciently low specific gravities but because of the presence of substantial proportions of normally solid paraffins such as paraffin or other wax, the solvent renders the recovered oils fluid at normal temperatures, and therefore susceptible to separation by centrifuging. The recovered mixture is also pumpable and can be transported or stored as a liquid without having to heat it.

The amount of solvent or diluent will vary with the type of shale being treated and the character of the hydrocarbons and other organic material in the shale oil. Factors to take into consideration are the degree and ease of solubility, the amount of bituminous material present, the density, fluidity and melting point of the bituminous material recovered, the specific gravity of the diluent and the viscosity of the resultant mixture of diluent and oil. The best separation takes place when the specific gravity of the bitumen is reduced to between 0.79 and 0.95 providing, of course, that the resultant recovered oil is fluid. If the oil separated is fluid at the temperature of separation and has a sufficiently low viscosity so that it will flow readily, and if it naturally has a specific gravity within the range of about 0.79 to about 0.95, it is un necessary to add the diluent.

In terms of percent by weight of the raw shale, the kerosene or other diluent may range from about 10% by Weight to about 30% by Weight, although more may be employed if desired or if necessary to render the oil sufliciently fluid for centrifuging. The shales contain varying amounts of recoverable oil, say 8--15%. The added diluent may amount to 0.5 to 2 times the volume of oil in the shale depending on how much is necessary to render the mixture fluid at the operating temperature.

It should be borne in mind that this is not a solvent extraction process even though the shale oil and diluent dissolve in one another. The diluent serves the primary purpose of .puttingthe oil in a physical condition which makes it possible to effect a substantially complete physical separation of solids-free oil by a process about to be described ingreater detail.

A large excess of water is now added to the mixture of raw shale, wetting agent, and diluent, when one is used. This must be suflicient to completely saturate the powdered shale and to render the settled solids fiuid enough for separation as a slurry. Additional water must be added, suflicient to provide a continuous water layer or barrier between the settled solids layer and the oil layer in the centrifuge so as to prevent any contact between the solids and the oil once the separation has been effected. If the oil and solids are recontacted, separation is rendered ditficult or impossible. The water barrier when the three layer system has formed in the centrifuge, should be at least one inch thick and usually is much thicker.

It is generally preferred to add the diluent and then add the aqueous phase or to add the two simultaneously. However, the aqueous phase may be added first providing the mixture is agitated to provide initimate contact of the diluent with the oil-bearing particles. The order of addition will depend in part upon the character of the shale being treated. In some instances it does not appear to be critical while in other instances better results are obtained by adding the diluent before adding the Water in order to obtain the maximum recovery.

Under some circumstances it is desirable to add the diluent before the mixture has been cooled to the centrifuging temperature, care being taken, however, to maintain a vapor tight system and to maintain sufilcient pressure so that the diluent does not vaporize substantially. This seems to assist in effecting solution of the oil and diluent.

The amount of water added is critical. In general, at least two volumes of aqueous phase are employed per volume of the shale undergoing treatment. The range may be from about 2 to about 5 volumes of aqueous phase per volume of disintegrated shale. The operation can be carried out in either a batch or continuous operation. In a typical operation, the diluent is added to the finely divided solids and thoroughly mixed so as to contact the oil and the diluent and to permit them to go into solution. Tl'llS mixture may be added to the aqueous phase or vice versa, with stirring to form and maintain a slurry. This is usually passed immediately to a centrifuge.

As an example of the amount of water which may be used the volume of voids between the settled solid particles may equal, for example, 40% of the volume of the solid particles on an oil-free basis. The oil may occupy 15% of these voids. Assume that an amount of diluent equal to the volume of contained oil, i.e. 15%, is added. Thus, on the basis of 100 volumes of original shale particles, 40 volumes would represent the voids, 15 volumes of which would be occupied by the raw oil and 15 volumes by the diluent. The solids, oil and diluent would occupy 90 volumes. If water, two times the original volume of the sand, is added, volumes would occupy the remaining voids. If all of the diluted oil is displaced by the water during the centrifuging, then 40 volumes of the aqueous phase would be required to just fill the resultant voids, leaving 160 volumes to form a water barrier between the oil'free solids and the oil layer. This proportion of water is equal to 1.6 times the volume occupied by the original shale particles, meaning that the water barrier is about 1.6times the depth of the sand. Therefore, for a good separation on a batch basis, the barrier should be approximately 1.6 times the depth of the solid particles and may extend up to about two or three times or more, although there appears to be no particular advantage in increased depth of water in such batch operations.

On a commercial basis, the operation is conducted continuously. Under these conditions the proportions of aqueous phase to disintegrated oil-shale plus diluent is somewhat different. Outlets are provided by nozzles in the periphery of the centrifuge bowl and by discharge rings so that there is a continuous discharge of 1), a slurry of solid material and water, (2) water, which may contain very fine particles of suspended solid materials, and (3) the oil layer substantially free of water and solids.

In such a continuous machine the raw slurry is fed into a central portion of the machine so that it is discharged into the water barrier. The mixture must pass through the water layer before it reaches the periphery of the bowl. This exerts a substantial and important physical stripping action due to the resistance of the water to pa'ssage of the solid (particles whereby the fluid diluted oil layer is stripped from the particles by the frictional action. A second oil-displacing effect is caused by the squeezing action brought about by the pressure exerted on the films of oil by the water. Since the latter has the higher specific gravity the augmented force exerted by the water overcomes the adhesive forces holding the oil to the particles and displaces it. The result is that all or substantially all of the oil is displaced from the sand and because of the difference in specific gravity and of the centrifugal action, the oil is forced inwardly through the Water barrier to form an overlying diluted oil layer.

Since water, as well as water and finely divided solids, must be removed from the machine it is evident that the proportion of water to the shale mixture charged must be greater in this type of operation than in the batch operation because some of the water must be used to assist in continuously removing the solids. The maximum amount of solids which can be discharged through the solids port is equal to about 60% in settled volume of the total passing through the outlet nozzle. Therefore, the minimum Water requirement merely to discharge the clean solids would be about 40% of the total volume of the solids-water discharge plus the amount required to fill the voids which is about 40% of the dry, oil-free solids volume. Therefore, the amount of water required for thepurpose of discharging the solids is approximately 1.7 times the volume of the dry solids. In addition to this, sufficient water must be supplied to provide the water barrier referred to above. Therefore, for continuous operation the minimum of aqueous phase to be fed with the solids-oil mixture would be in excess of 1.7 times the volume of the clean solids, plus sufficient water to provide the necessary barrier between the oil layer and the solids layer. Since the depth of the barrier should be sufiicient to prevent recontact of oil with the sand, the practical lower limit for continuous operation is about 2 volumes of water to one volume of disintegrated sand and is preferably about 2.5 to 5 or more.

'It has been determined that there is a relationship between the number of Gs applied and the depth of the water barrier (Gs equal apparent weight of the solids in an operating centrifuge, divided by its actual weight).

Thus, the product of the thickness of the water barrier in inches and the GS of acceleration equal a constant which has been found to be 2500. In order to minimize erosion in the machine, the combination of Gs and the depth of water barrier should be one which will completely strip the sand with the least possible number of Gs effective to permit efiicient separation of the oil. Therefore, in a continuous machine, the water barrier should be as deep as it is practical to make it in order to reduce the Gs and consequently minimize erosion. It is desirable to make the machines as large as possible in order to minimize their speed. Machines have been .built and tested which provide water barriers of from one inch up to 12 inches in thickness. However, larger machines providing water barriers of 2430 inches are possible. The limiting factors being the strength of materials combined with good engineering design.

The minimum water requirements in such a continu- 7 ous operation may be expressed as approximately four times the volume required to saturate the sand and is preferably somewhat greater than this.

Since the solids in the mixtures to be separated according to this invention are more finely divided than the major proportion of the sand in the tar sands referred to in my copending application, the peripheral speeds in the centrifuge are somewhat higher in order to effect complete separation of the oil from the fine solids than would be the case with coarser sand particles.

The temperature at which the separation is effected is not so critical as to require exact control. It must be above the freezing point of the aqueous phase and below the boiling point of water. Ordinarily it is carried out at the temperature of the natural water supply. In sum mer months or in warm climates no special temperature control is needed. Since the temperature of the disintegrated shale must be reduced from that of the disintegration step, the cold water can be added to the still warm shale to provide a temperature best adapted for the separation, say 60100 F. If the oil is highly viscous or tends to solidify at these temperatures, a higher temperature up to 200 F., but usually not above about 150l60 F., may be used to cause it to remain fluid. Increased temperatures tend to lower the viscosity of both the oil and the water but do not change their relative specific gravity. The effect on the viscosity of the oil is, of course, more pronounced than on water. Hence, if the separation is carried out at mildly elevated temperatures, not only is the oil stripped more readily from the particles but it will pass through the water barrier at a considerably faster rate than at the lower temperatures, thereby increasing the capacity of the centrifuge.

The surface active agent capable of lowering the surface tension of the aqueous phase and capable of increasing the wettability of the solids by water is employed. This should not be of a type or used in an amount which would cause emulsion formation. It can be added to the powder as a solid or in solution, or can be dissolved or dispersed in the aqueous phase.

In the natural state the surface tension of the oil constituent is usually lower than the surface tension of the water, probably because of the high mineral content of the waters found in association with bituminous materials in nature. If this natural relationship is reversed and the surface tension of the water reduced below that of the oil, more thorough separation will take place and the time required for centrifuging will be substantially reduced.

Among the surface tension agents which may be used are those which are well known and commercially available. Fatty alcohol sulfates such as those marketed under the trade name Dreft may be employed. A sulfated mixture of fatty acid monoglycerides such as those marketed as "Vel" and Halo, or the ester of sodium sulfosuccinic acid known as Aerosol" may be used together with a solubilizing agent such as methyl hydrate. Although certain water soluble soaps may be used, care must be exercised in the proportions employed to guard against emulsion formation. One particularly useful agent is Ethomid HT/60 which is a mixture of monoand di-substituted amides made by treating unsubstituted amides with ethylene oxide. This is sold by the Chemical Division of Armour & Co., Chicago, Illinois.

The proportion of surface active agent is small and hence does not materially raise production costs. Approximately 0.0025% of surface active agent by weight of the inorganic solids is generally sufiicient and is usually less than about 0.01%. This may vary on either side of this amount and the exact proportion to be used is readily determinable by making a trial run.

Instead of water alone saline solutions may be used. These may comprise neutral salts which are soluble in water and which have the effect of increasing the specific gravity of the water and may, at the same time, act as an electrolyte. Sodium chloride and calcium chloride are examples of readily and cheaply available materials which can be used. Other salts, particularly neutral salts, may be employed but in general are more expensive.

Since saline solutions tend to increase the surface tension of the water, it is preferred to use them with a surface-active agent such as one of those previously listed.

In certain instances it is desirable to effect a major separation of the larger particles of solids, if there be any present, in a centrifuge or cyclone at relatively low speeds. Under these conditions the oil may contain some very finely divided suspended material although in comparatively small amounts. This oil, together with sufficient water to form a suitable barrier, may be subjected to a final cleaning treatment in a higher speed centrifuge whereby the remaining solids and Water are separated.

The final oil thus recovered may be treated according to normal refinery practice to produce desirable products. This includes distillation into various fractions useful as diesel fuels, furnace distillates, naphthas and the like. Normally the lower boiling constituents may be separated by atmospheric or vacuum fractional distillation, particularly to remove fractions containing parafiin wax. The parafiin wax may be recovered by known methods and purified. Suitable methods are known in the petroleum industry. Likewise, shale oil resins useful for many purposes may be recovered from the residue by known methods.

Under some conditions all or certain fractions of the recovered shale oil may be subjected to coking to produce gas and lower boiling constituents plus coke which is useful as fuel, for example, to furnish heat for the disintegration step. These fractions may be refined to recover valuable products. Under other conditions the recovered oil with or without preliminary separation of the diluent or solvent may be subjected to a cracking operation to produce gas, gasoline and the like.

When the oils are coked or cracked there is usually a considerable amount of ammonia evolved because the relatively high nitrogen content of the shale oil is broken down by heat. Ammonia may be recovered from the gases, for example by passing them through sulfuric acid or nitric acid, the ammonia being recovered as a salt which is useful in fertilizers and for many other purposes.

When an oil shale such as that found in Colorado or Wyoming and containing about 15% of oil is treated with superheated steam at about 700 F. and 3000 p.s.i.g. pressure, it disintegrates into a fine powder resembling talcum in particle size. This is cooled at about F. and a cracked diluent of the kerosene boiling range is added in amount proportionately equal to the volume of oil in the shale, and thoroughly mixed. Two volumes of water are added per volume of powder and agitated to form a slurry. Upon centrifuging, a substantially solids-free diluted oil is recovered. The recovery of shale oil may amount to 90% or more of that in the original shale.

The initial cooling may be effected by passing low temperature steam through the powder, the pressure being reduced. The first effluent vapors may be condensed by scrubbing with dilute sulfuric acid which reacts with ammonia formed during the disintegration step. The remainder which has become somewhat superheated may be further superheated for use in the process, or passed into direct or indirect heat exchange with fresh shale to recover as much heat as possible.

I claim as my invention:

1. A process for recovering shale oil which comprises heating a pyrobituminous shale in the presence of superheated steam at a temperature of about 570 to about 1200' F. and a pressure above p.s.i.g. but below the critical pressure of steam, for a time sufficient to disintegrate it to a powder, cooling the powder to a temperature below the boiling point of water, mixing it with a dispersing agent and at least about two volumes of water per volume of shale, and separating and recovering oil substantially free of solids, by means of centrifugal force.

2. The process of claim 1 wherein a hydrocarbon diluent is admixed with the powdered shale prior to the centrifugal separation, in an amount to reduce the specific gravity of oil in said shale to a point in the range of about 0.75 to about 0.95, to reduce its viscosity and to render it free flowing at temperatures in the range of 10 10 ture of recovered oil and hydrocarbons boiling below the initial boiling point of the recovered oil.

7. The process of claim 2 wherein the diluent boils in the range of about 350 to about 750 F.

8. The process of claim 2 in which the amount of water added is about 2 to about 5 volumes per volume of disintegrated shale.

9. The process of claim 2 wherein the water phase is a solution of a neutral salt.

10. The process of claim 2 wherein the aqueous phase is in an amount to provide a barrier at least one inch thick between the layer of solids and the layer of oil produced in the centrifugal separation step.

References Cited in the file of this patent UNITED STATES PATENTS 1,396,173 Fenton Nov. 8, 1921 2,793,104 Rees May 21, 1957 2,825,677 Coulson Mar. 4, 1958 

1. A PROCESS FOR RECOVERING SHALE OIL WHICH COMPRISES HEATING A PYROBITUMINOUS SHALE IN THE PRESENCE OF SUPERHEATED STEAM AT A TEMPERATURE OF ABOUT 570* OF ABOUT 1200*F. AND A PRESSURE ABOVE 150 P.S.I.G. BUT BELOW THE CRITICAL PRESSURE OF STEAM, FOR A TIME SUFFICIENT TO DISINTEGRATE IT TO A POWDER, COOLING THE POWDER TO A TEMPERATURE BELOW BOILING POINT OF WATER, MIXING IT WITH A DISPERSING AGENT AND AT LEAST ABOUT TWO VOLUMES OF WATER PER VOLUME OF SHALE, AND SEPARATING AND RECOVERING OIL SUBSTANTIALLY FREE OF SOLIDS, BY MEANS OF CENTRIFUGAL FORCE. 